The present disclosure is related generally to the measurement of vehicle wheel alignment values, and in particular, to methods and apparatus for automating procedures for obtaining measurements of vehicle wheel alignment, including rolling compensation and caster steering procedures.
When a vehicle is brought to a shop for a wheel alignment service, a number of preliminary procedures are required to be carried out prior to the actual adjustment of any wheel alignment angles. Many of these procedures are independent of the specific type or model of vehicle undergoing the wheel alignment service. For example, when a vehicle is brought into a service bay, alignment sensors or targets are typically attached to the vehicle wheels and compensated for any mounting misalignment from the rotational axis of each wheel. Traditionally, a rolling compensation procedure is carried out after the sensors or targets are mounted to the vehicle wheels, wherein a technician manually pushes or pulls the vehicle to induce a rolling movement of the vehicle over a short distance. By monitoring the translational and rotational movement of the sensors or targets attached to the wheels, the vehicle wheel alignment system determines any necessary compensation values which will be used in any subsequent procedures associated with the vehicle wheel alignment service. Manually imparting the necessary rolling movement to the vehicle by a technician risks serious injury. If the vehicle is heavy or has a high rolling resistance, the technician may be required to exert a significant push to the vehicle, risking personal injury. Correspondingly, if the vehicle is of a lighter weight, or quickly overcomes any rolling resistance, too much exerted force could potentially cause the vehicle to roll too far, or even off of a lift rack on which it may be resting, resulting in damage to the vehicle and risk of injury to bystanders.
A second procedure which is often carried out prior to actual adjustment of any wheel alignment angles is the caster steer procedure, which facilitates calculation of a steered wheel's caster angle based on either changes in the camber angle of the steered wheel or, for machine-vision based alignment systems, from a minimum of two different images of the wheel or target as the toe angle of the wheel changes during steering movement. Typically, during a vehicle wheel alignment adjustment service procedure, any steering angle changes are made by turning the vehicle steering wheel from the driver's seat position, and not by turning the vehicle wheels directly, resulting in lost time to complete the alignment adjustment procedure, additional physical effort, and an inconvenience to the alignment technician who is required to reach into or climb in and out of the vehicle. Furthermore, for some wheel alignment angle adjustments, the operator is required to initially steer the vehicle wheels to a straight ahead position, or to another selected position, from the driver's seat, make the necessary adjustments causing the steered location of the vehicle wheels to change, and then return to the driver's seat to steer the wheels back to the selected position to continue making adjustments of the alignment angles. This time consuming process may be repeated several times to verify the adjustments of the alignment angles results in the alignment angles being within specification.
Accordingly, in order to automate and expedite a vehicle wheel alignment service procedure for a vehicle, it would be advantageous to provide a means by which a number of the common and generic procedures may be automatically carried out by the vehicle wheel alignment service system. In particular, it would be advantageous to provide a mechanism to automating the rolling movement of a vehicle required to complete the rolling compensation procedures, to provide a mechanism for automating the steering movement of the steered vehicle wheels required to complete the caster steer procedures, as well as other procedures which require steered movement of the wheels.